On 21/02/14 01:23, Christoffer Dall wrote:
> On Thu, Feb 20, 2014 at 03:26:54PM +0000, Marc Zyngier wrote:
>> Commit 1fcf7ce0c602 (arm: kvm: implement CPU PM notifier) added
>> support for CPU power-management, using a cpu_nofigier to re-init
>> KVM on a CPU that entered CPU idle.
>>
>> The code assumed that a CPU entering idle would actually be powered
>> off, loosing its state entierely, and would then need to be
>> reinitialized. It turns out that this is not always the case, and
>> some HW performs CPU PM without actually killing the core. In this
>> case, we try to reinitialize KVM while it still live. It ends up
>> badly, as reported by Andre Przywara (using a Calxeda Midway):
>>
>> [ 3.663897] Kernel panic - not syncing: unexpected prefetch abort in Hyp mode at: 0x685760
>> [ 3.663897] unexpected data abort in Hyp mode at: 0xc067d150
>> [ 3.663897] unexpected HVC/SVC trap in Hyp mode at: 0xc0901dd0
>>
>> The trick here is to detect if we've been through a full re-init or
>> not by looking at HVBAR (VBAR_EL2 on arm64). This involves
>> implementing the backend for __hyp_get_vectors in the main KVM HYP
>> code (rather small), and checking the return value against the
>> default one when the CPU notifier is called on CPU_PM_EXIT.
>
> This definitely looks correct and is a good solution, so
>
> Acked-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>
> But see my usual request below.
>
>>
>> Reported-by: Andre Przywara <osp@xxxxxxxxx>
>> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
>> Cc: Rob Herring <rob.herring@xxxxxxxxxx>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>> arch/arm/kvm/arm.c | 3 ++-
>> arch/arm/kvm/interrupts.S | 7 ++++++-
>> arch/arm64/kvm/hyp.S | 9 +++++++--
>> 3 files changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index 1d8248e..bd18bb8 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -878,7 +878,8 @@ static int hyp_init_cpu_pm_notifier(struct notifier_block *self,
>> unsigned long cmd,
>> void *v)
>> {
>> - if (cmd == CPU_PM_EXIT) {
>> + if (cmd == CPU_PM_EXIT &&
>> + __hyp_get_vectors() == hyp_default_vectors) {
>> cpu_init_hyp_mode(NULL);
>> return NOTIFY_OK;
>> }
>> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
>> index ddc1553..9b0ff68 100644
>> --- a/arch/arm/kvm/interrupts.S
>> +++ b/arch/arm/kvm/interrupts.S
>> @@ -363,6 +363,11 @@ hyp_hvc:
>> host_switch_to_hyp:
>> pop {r0, r1, r2}
>>
>> + /* Check for __hyp_get_vectors */
>> + cmp r0, #-1
>> + mrceq p15, 4, r0, c12, c0, 0 @ get HVBAR
>> + beq 1f
>> +
>
> I hate to be a stickler about this, but I think the comment explaining
> the KVM/ARM Hypervisor ABI needs to be tweaked (it may have been too
> verbose to begin with), but it should be updated at least to specify the
> special-case handling of r0. I think a small comment somewhere on the
> arm64 part would be similarly nice, but it's not something that should
> hold this patch back.
Good point. I'll add it and repost the patch.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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